Automatic transmission fluids with phthalic acid corrosion inhibitor

Abstract

A phthalic acid such as terephthalic acid is made soluble in an oil of lubricating viscosity by first mixing it with at least one phosphorus compound. The resulting product is useful for reducing corrosion in a transmission lubricant.

1. A composition useful for lubricant applications, comprising:
 (a) about 0.0001 to about 0.05 percent by weight of terephthalic acid or a salt thereof; and 
 (b) (i) phosphoric acid or phosphorous acid and (ii) a dialkyl hydrogen phosphite; and 
 (c) a dispersant; and 
 (d) an oil of lubricating viscosity; 
 wherein said composition is prepared by mixing the terephthalic acid or salt thereof with (b)(ii) the dialkyl hydrogen phosphite, without an inorganic phosphorus acid or salt, and thereafter adding (b)(i) the phosphoric acid or phosphorous acid. 
 
     
     
       2. The composition of  claim 1  wherein the terephthalic acid or salt is terephthalic acid. 
     
     
       3. The composition of  claim 1  wherein the amount of the terephthalic acid is about 0.001 percent by weight to about 0.05 percent by weight of the composition. 
     
     
       4. The composition of  claim 1  wherein the dialkyl hydrogen phosphite is di-n-butyl hydrogen phosphite. 
     
     
       5. The composition of  claim 1  wherein the total amount of the dialkyl hydrogen phosphite is about 0.005 percent by weight to about 2.0 percent by weight. 
     
     
       6. The composition of  claim 1  wherein the dispersant is a succinimide dispersant. 
     
     
       7. The composition of  claim 1  wherein the amount of the dispersant is about 1.2 to about 4.8 percent by weight. 
     
     
       8. The composition of  claim 1  wherein (a) the terephthalic acid or salt and (b) the combination of phosphoric acid or phosphorous acid and the dialkyl hydrogen phosphite are present in a weight ratio (a):(b) of about 0.005:1 to about 0.5:1. 
     
     
       9. The composition of  claim 1  wherein the amount of the oil of lubricating viscosity is an amount suitable to provide an oil-containing concentrate. 
     
     
       10. The composition of  claim 1  wherein the amount of the oil of lubricating viscosity is an amount suitable to provide a fully formulated lubricant. 
     
     
       11. The composition of  claim 1  further comprising a detergent. 
     
     
       12. The composition of  claim 1  further comprising a borate ester friction modifier. 
     
     
       13. A method for preparing a soluble composition of about 0.0001 to about 0.05 percent by weight of (a) terephthalic acid in an oil of lubricating viscosity, comprising:
 mixing said terephthalic acid with (b) (ii) a dialkyl hydrogen phosphite, and thereafter adding (b)(i) phosphoric acid or phosphorous acid (d) said oil of lubricating viscosity, and (c) a dispersant. 
 
     
     
       14. The method of  claim 13  wherein the terephthalic acid is mixed with a dialkyl hydrogen phosphite with heating until the terephthalic acid is dissolved. 
     
     
       15. The method of  claim 13  wherein the terephthalic acid is not pre-reacted with a dispersant prior to mixing with the oil of lubricating viscosity (d). 
     
     
       16. The method of  claim 13  wherein the terephthalic acid (a) is combined with (b) the phosphoric acid or phosphorous acid and the dialkyl hydrogen phosphite in a weight ratio (a):(b) of about 0.005:1 to about 0.5:1. 
     
     
       17. The method of  claim 13 , further comprising including in the product thereof at least one detergent, dispersant, or friction modifier. 
     
     
       18. A method for reducing the corrosive properties of a transmission lubricant which comprises adding thereto the composition of  claim 1 . 
     
     
       19. A method for lubricating a transmission, comprising supplying thereto the composition of  claim 1 . 
     
     
       20. The composition of  claim 1  wherein the mixing of the terephthalic acid or salt with the dialkyl hydrogen phosphite is accompanied by heating at about 60° C. to about 150° C. 
     
     
       21. The method of  claim 14  wherein the heating is at about 60° C. to about 159° C. 
     
     
       22. A composition useful for lubricant applications, comprising:
 (a) about 0.001 to about 0.05 percent by weight of terephthalic acid or a salt thereof; and 
 (b) about 0.01 to about 1.0 percent by weight of: (i) phosphoric acid or phosphorous acid and (ii) a dialkyl hydrogen phosphite; and 
 (c) a dispersant; and 
 (d) an oil of lubricating viscosity; 
 wherein said composition is prepared by mixing the terephthalic acid or salt thereof with (b)(ii) the dialkyl hydrogen phosphite without an inorganic phosphorus acid or salt, said mixing accompanied by heating at about 60° C. to about 150° C., and thereafter adding (b)(i) the phosphoric acid or phosphorous acid.